In many machine-readable data encoding methods (bar code, MaxiCode, etc.), it is necessary for the encoded mark to be in the proper orientation or alignment to be accurately decoded. A variety of methods have been patented that attempt to solve this problem. U.S. Pat. No. 3,585,366 to Kern teaches a circular code that requires the user to place the point of a reading device in the center of the circular code. Alignment is assured by the point of the reading device protruding into a hole or dimple in the surface on which the circular code is affixed. Kern also uses bar-shaped indicia to represent the data encoded in the circular code.
U.S. Pat. No. 3,752,961 to Torrey teaches the use of a circular bar code. To decode the circular bar code, the proper orientation must be obtained, so that the information can be decoded in the correct order. Torrey decodes the circular barcode starting at a particular point and proceeding in a clockwise manner.
U.S. Pat. No. 4,308,455 to Bullis et al. teaches decoding a “CODABAR” or “Code39” which is an ordered arrangement of four bars and three spaces. Before accurate decoding can begin, a “start” code must be identified to insure accurate alignment and orientation of the barcode.
Circular barcodes used only for alignment purposes are disclosed in U.S. Pat. No. 6,088,482 to He et al.
More recent efforts to solve the orientation and alignment problems associated with barcodes still require configurations that identify the beginning and end of the bar code to insure proper orientation and alignment. U.S. Pat. No. 5,861,613 to Apelberg et al. teaches the use of a circular barcode with a relatively large “quiet zone” between the barcodes “start” and “stop” codes. By having a relatively large quiet zone, Apelberg insures that no matter how misaligned the reader is from the circular barcode the start of the barcode can found.
U.S. Pat. No. 3,643,068 to Mohan et al. has several circular codes including some that use “end cycles” that are similar to Apelberg's “quiet zones”.
Another problem is placing a bar code in a small compact space. Since typical bar codes are horizontal, the amount of space in which they can fit is limited by the amount of horizontal space available on the object to be marked. Furthermore, a typically bar code can only encode approximately ten digits per inch.
In light of the problems associated with barcodes (horizontal or circular) attempts have been made to use dot (filled-in circles) codes as an alternative. U.S. Pat. No. 6,533,182 to Ohshima et al. utilizes dots arranged horizontally in place of bar codes, but requires the dot code to be bordered at the end of the horizontal dot code by timing marks. The timing marks are continuous columns of dots that are used by the reader to insure accurate decoding. U.S. Pat. No. 6,601,772 to Rubin et al. uses a matrix code in the shape of a circle. The code includes three curved targets surrounded by reserved white space and hexagonal cells laid out in a closely-packed hexagonal grid. The curved targets, reserved white space, and hexagonal cells all are used in some manner for targeting or alignment purposes. U.S. Pat. No. 6,663,008 to Pettersson et al. discloses a dot code that is offset from a nominal position along a raster scan, the location of the dot indicating the value of the dot. The raster scan can be in the shape of a square, triangular or hexagonal matrix. The assignee of the Pettersson et al. patent discloses a dot code in WIPO publication, WO 03/107265 A1, which utilizes dots of various diameters to convey certain information. Other examples of dot-code matrix type inventions are U.S. Pat. No. 6,185,405 to Yoshioka and U.S. Pat. No. 6,116,507 to Fukuda et al.
U.S. Pat. No. 6,478,232 to Dowling et al. discloses a dot code that has dots located in special regions of a circular array. However, Dowling also resorts to alignment markings that appear outside the circular array. Dowling requires that lines connect the dots of the circular array, indicating a sequence in which the dots were placed. The sequence is then used for decoding purposes.
U.S. Pat. No. 3,643,068 to Mohan et al. also discloses a circular code for representing a packed binary coded decimal, but the amount of data is limited because each circular band is crossed by a radial wedge that separates the circular bands into regions of equal size. Furthermore, Mohan requires that the data coding marks be in a specific spatial orientation to one another within the circular bands.
A need exists for an improved data encoding mark that provides an omni-directional reading capability and ease of decoding.